According to Newton's first law inertial motion happens without interaction. What moves the inertially moving object? In Aristotelian mechanics inertial motion

According to Newton's first law inertial motion happens without interaction. What moves the inertially moving object? In Aristotelian mechanics inertial motion stops shortly after beginning, so for sustained motion the object must be moved by another. Falling leaf is not inertial motion, it's pulled by gravity, Aristotle didn't know about gravity, but Aquinas probably did as round Earth theory required the concept of gravity.